MRI systems employ static magnets which create a nominally homogeneous magnetic field in an imaging area. During the imaging procedure, gradient coils, which alter the static magnetic field by generating gradient magnetic fields in one of three orthogonal directions, rapidly switch on and off to isolate a particular section of the human body for imaging. The image information is obtained by transmitting RF signals to the human body in the imaging area to excite selected human nuclei and thereafter sensing the RF signals emitted from the nuclei as they relax from their excited state.
The gradient coils and RF transmission and reception coils are generally housed in the MRI system in close proximity to One another around the imaging area. Unfortunately, due to this proximity, the gradient coils can couple with the RF coils during RF transmission and reception, causing losses in the RF signals and corresponding reductions in the RF coil Q values. For these reasons, various shields have been devised to effectively decouple the gradient coil windings from the RF coil windings to reduce losses during RF transmission and reception and to improve RF coil Q.
One such prior RF shield for use in MRI systems with a cylindrical geometry is made with a flexible PC board having copper cladding on both sides of the board. Alternating slits in the front and back sides of the PC board divide the copper cladding on each side into a number of electrically isolated conductive panels. The electrical isolations reduce the effect of eddy currents generated in the PC board. Yet, the PC board is a contiguous conductor to RF signals since the thin substrate between the panels forms capacitors (i.e., short circuits to RF signals) between the alternating layers of conducting panels on the front and back sides of the board.